This invention relates to process control and, more particularly, to improved apparatus for actuating a process controller responsive to a movable member, such as a machine tool slide.
Process controllers are used in many fields to carry out automatic operation of a process. For example, process controllers automatically operate machine tools responsive to cam actuated mechanical limit switches that sense the position of the machine tool slide on which the work piece is supported. A limit switch is actuated when the slide is positioned between limits, inside of which a particular operation is to be performed; while the limit switch is so actuated, it supplies an electrical activating signal to a particular input of the process controller, which carries out the desired operation.
In machine tools that perform a large number of operations, many limit switches must be coupled to the slide to activate the process controller. These limit switches are costly and bulky and require continual adjustment as the moving parts wear. Prior to initial start-up on a series of operations, delicate fine tuning of the limit switch position is necessary to ensure satisfactory operation. When the machine tool is reprogrammed to perform different operations, the limit switches must be repositioned anew.